Data is presented for a complex structural and compositional modulation in the perovskite. This modulation creates a large supercell ( is the lattice parameter of the cubic perovskite aristotype) containing ordered regions with doubled (110) d-spacings in the a-b plane separated by two-dimensional periodic antiphase boundaries and accompanied by a nanocheckerboard pattern. Faint periodic modulations in Z-contrast images suggest an associated periodic variation in composition. The presence of a sodium rich impurity implies the composition of the stable perovskite is nonstoichiometric.

The material gain of equal width InGaAsP/InGaAsP multi–quantum well active layers is calculated solving the Lüttinger–Kohn Hamiltonian, including tetragonal strain and confinement effects. The calculated optical bandwidth reaches 150 nm with a maximum polarization sensitivity of 1 dB between transverse electric (TE) and transverse magnetic (TM) emission over the −3 dB optical bandwidth. The corresponding device characterized by amplified spontaneous emission measurements shows an optical bandwidth with constant TE/TM ratio of almost 100 nm which can be improved up to 113 nm by increasing the barrier material band gap energy. Further enlargement of the optical bandwidth is expected by reducing the quantum well width.

The ultraviolet-infrared transmittance spectra of nanocrystalline film have been studied in the temperature range 5.3–300 K. A redshift trend of the absorption edge and optical constants with increasing the temperature can be observed. Four interband electronic transitions can be uniquely assigned and strongly depend on the temperature. Moreover, two magnetic transitions located at about 150 and 200 K have been observed and can be interpreted as spin-reorientation transitions. It was found that the optical band gap decreases from to with increasing the temperature due to the modification of the electron-phonon interactions.

Two-color pump-probe measurements are used to study the carrier dynamics of InAs/GaAs quantum dots in a waveguide structure under reverse bias conditions. For the case of initially populating the ground state(GS), we find relaxation dynamics that include both absorptive and bleaching components in the excited state(ES) wavelength range. We reproduce the main features of this induced absorption dynamics using a simple model with an additional term for induced absorption at the ES due to carriers injected at the GS. The induced absorption dynamics includes multiple recovery timescales which can be attributed to phonon-assisted processes of GS/ES interaction.

Pumping a nonlinear germanosilicate fiber with intense near-infrared femtosecond laser pulses for supercontinuum generation may invoke multiphoton-assisted photosensitivity of glasses to write a long-period fiber grating. In sharp contrast to the spontaneous formation of a Hill grating that resonates with the writing wavelength through first-order diffraction, the long-period fiber grating resonates with the writing wavelength through second-order diffraction. This finding highlights the surprising light-matter interaction in a waveguide.

We propose a model to better investigate InGaN light-emitting diode(LED) internal efficiency by extending beyond the usual total carrier density rate equation approach. To illustrate its capability, the model is applied to study intrinsic performance differences between violet and green LEDs. The simulations show performance differences, at different current densities and temperatures, arising from variations in spontaneous emission and heat loss rates. By tracking the momentum-resolved carrier populations, these rate changes are, in turn, traced to differences in bandstructure and plasma heating. The latter leads to carrier distributions that deviate from the quasiequilibrium ones at lattice temperature.

We achieved high-sensitivity, rapid-response detection of terahertz (THz) waves using an organic nonlinear optical crystal, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Nonlinear up-conversion in the crystal resulted in a shift of THz waves to near-infraredradiation at room temperature. A minimum THz-wave peak power of about was measured at 19.2 THz by detecting the up-converted optical signal with an InGaAs-based photodetector. A noise equivalent power of about was estimated in this experiment. Optimum conditions were obtained for THz-wave detection using a DAST crystal.

Electronic and optical properties of strain-compensated InGaN/InGaN/MgZnO quantum well(QW) structures using a MgZnO substrate are investigated using the multiband effective mass theory. A strain-compensated InGaN/InGaN/MgZnO QW structure with a larger strain shows larger matrix element than that with a smaller strain. The spontaneous emission peak rapidly increases with increasing compressive strain because the matrix element is enhanced for the strain-compensated QW structure with a larger strain. In addition, we find that the strain-compensated QW structure with the larger Mg composition in the substrate has greater spontaneous emission peak than the strain-compensated QW structure with the smaller Mg composition in the substrate.

A photonic crystal substrate exhibiting resonant enhancement of multiple fluorophores has been demonstrated. The device, fabricated uniformly from plastic materials over a surface area by nanoreplica molding, utilizes two distinct resonant modes to enhance electric field stimulation of a dye excited by a laser (cyanine-5) and a dye excited by a laser (cyanine-3). Resonant coupling of the laser excitation to the photonic crystalsurface is obtained for each wavelength at a distinct incident angle. Compared to detection of a dye-labeled protein on an ordinary glass surface, the photonic crystalsurface exhibited a 32× increase in fluorescent signal intensity for cyanine-5 conjugated streptavidin labeling, while a 25× increase was obtained for cyanine-3 conjugated streptavidin labeling. The photonic crystal is capable of amplifying the output of any fluorescent dye with an excitation wavelength in the range by selection of an appropriate incident angle. The device is designed for biological assays that utilize multiple fluorescent dyes within a single imaged area, such as gene expression microarrays.

An electrically tunable polymer microring resonator of large tunability and low applied voltage is demonstrated using active liquid crystal (LC)cladding. A large tuning range of 0.73 nm is achieved due to more homogenous LC molecular alignment and enhanced interaction of the light with the LCcladding in the simplified polymer waveguide structure. The operating voltage decreases to 10 V with a threshold of only 3 V by the utilization of interdigital electrodes.

We report temperature-dependentabsorption recovery times in an InAs p-i-n ridge waveguide quantum-dot modulator under low reverse bias, investigated via subpicosecond pump-probe measurements. The measured decrease in absorption recovery time with increasing temperature (293–319 K) is in excellent agreement with a thermionic emission model. A similar trend in pulse duration with increasing temperature is also observed from a two-section mode-locked quantum-dot laser fabricated from a similar epitaxial structure. These measurements confirm the key role of the absorber recovery time in the reduction in the pulses generated by two-section mode-locked quantum-dot lasers, both at room and elevated temperatures.

We propose and demonstrate the application of high-pressure water-vapor annealing (HWA) to siliconphotonic crystals for surface passivation. We find that the photoluminescence intensity from a sample treated with HWA is enhanced by a factor of . We confirm that this enhancement originates from a reduction in the surface-recombination velocity (SRV) by a factor of . The estimated SRV is as low as at room temperature. These results indicate that HWA is a promising approach for efficient surface passivation in siliconphotonicnanostructures.

Generally the gap voltage at the moment of arc initiation in a vacuum is significantly larger than the voltage in developed arcs. This phenomenon was studied here suggesting a physical model for initially triggered at the bulk cathodeplasma and then for appeared transient spot. The model allows calculating the transient energy flux to the cathode and the transient cathode potential drop (CPD). It was shown that the CPD at the moment of spot ignition is relatively large and significantly contributes to the arc voltage at arc ignition. The subsequent voltage decrease can be understood from the transient CPD behavior during arc development. The voltage oscillation in an arc was explained by suggested model taking into account the spot shifting on a cold location.

Aluminum hydroxide nanocrystals consisting of an amorphous shell and crystalline core are fabricated by pulsed laser ablation of an aluminum target in water. The colloid consisting of nanocrystals with a uniform size exhibits a size-independent photoluminescence(PL) band at . According to the PL excitation spectra and time-resolved PL decay analysis, this PL band originates from oxygen vacancies in the amorphous shell and Förster energy transfer occurs between the oxygen vacancy levels in the crystalline core and amorphous shell. These phenomena are found to alter the PL excitation spectra.

The effect of underlayer thin films on the sensitivity of Agnanorodsurface-enhanced Raman scattering(SERS) substrates was studied both theoretically and experimentally. With the same Agnanorodfilm, different materials (Ag, Al, Si, and Ti) with different thicknesses (25, 100, and 400 nm) were used as underlayers to alter the reflectivity systematically. The SERS intensity was found to increase linearly with the underlayer reflectivity, which can be explained by a modified Greenler’s model due to the contribution of reflected electric field from the substrate. This finding can be used to design high enhancement SERS substrates.

The shock-front structures of nanocrystallineAl are investigated in detail by exploring the relationship between the evolution of stress, particle velocity distributions, and the atomistic structures through molecular dynamics simulations. It is found that in nanocrystallineAl the contribution of grain boundary-mediated plasticity to the shock-front width is significant in comparison with dislocation-mediated plasticity. Due to different deformation mechanisms and time sequences, the shock front can be separated into following three stages: elastic, grain boundary dominated plasticity, and dislocation emission and propagation.

We have depositedthin films by pulsed laser deposition, changing the ratio of surface diffusivity to deposition flux (D/F) by adjusting substrate temperature and laser repetition rate. We show that persistent two-dimensional layer-by-layer growth, at least up to 30 nm, can be achieved by exploiting diffusion-limited growth (small D/F ratio), giving rise to atomically-flat epitaxialfilms. The results are of interest in spintronic applications such as tunnel magnetoresistance devices, and the approach presented here can be extended to other functional films of high surface energy.

A substrate coated with an achiral polyimide alignment layer was scribed with the stylus of an atomic force microscope having a line-to-line force profile . The strength of the resulting chiralsurface was examined using the nematic liquid crystal electroclinic effect induced by the surface. The magnitude of the electroclinic effect was found to increase with increasing scribing force, which suggests a method for controlling the chiral strength. Additionally, the electroclinic magnitude divided by the rms surface roughness was approximately constant with scribing force, suggesting that the azimuthal anchoring strength coefficient is nearly independent of the scribing force.

Several molecules are known to contain stable silicon double or triple bonds that are sterically protected by bulky side groups. Through first-principles computation, we demonstrate that well-defined bonds can also be stabilized in a prototypical crystalline Si structure: Schwarzite Si-168, when modest negative pressures are applied to a nanoscale porous framework. The -bonded Si-168 is thermodynamically preferred over diamondsilicon at a negative pressure of −2.5 GPa. Ab-initio molecular dynamics simulations of Si-168 at 1000 K reveal significant thermal stability. Si-168 is metallic at in density functional theory, but a gap (between -like and -like bands) opens around the Fermi level at the transition pressure of −2.5 GPa. Alternatively, a band gap buried below the Fermi level at can be accessed via hole doping in semiconducting .

We investigate two-dimensional boron transient diffusion in sub-micron scale patterns by plane view scanning capacitance microscopy (SCM). Submicron long strips and squares ion implantation windows of systematically varying sizes have been designed and fabricated. Boronion implantation and spike annealing were followed to activate the dopant and cause diffusion. Square opening windows show more enhanced diffusion than the long strip counterparts, especially at larger length scales. We explain the observation and fit the experimental data by a nonlinear logistics model. The implication to modern microelectronic circuit design and conventional dopant profiling methodology are discussed.

A small quantity of carbon nanotubes was dispersed in an achiral liquid crystal(LC), and the mixture was found to exhibit a weak degree of chirality. The induced chirality in the LC was probed by means of the electroclinic effect in the LC’s smectic- phase, which showed significant pretransitional behavior on approaching the smectic-–smectic- transition temperature from above. The results suggest that there is a net chirality associated with the carbon nanotubes, which is transmitted into the LC.